(a) Field of the Invention
The present invention relates to a method and an apparatus for generating a common signal which is a signal transmitted to omnidirection of the antennas; so commonly required for terminals in a multiple input multiple output (MIMO) system to transmit signal to the target terminal by making sharp radio beam.
(b) Description of the Related Art
Recently, a technology emerging as the strongest candidate technologies to satisfy requirements of a traffic increase in the fifth generation mobile communications may include multiple input multiple output (MIMO), that is, a massive MIMO technology which is an expansion of multiple antenna technology.
A system to which the massive MIMO is applied theoretically has several advantages in that fast fading is extinguished, throughput is increased, the number of service enabling terminals is increased regardless of a cell size, and the like. In addition, since the number of transmission RF paths and antennas is increased in the massive MIMO system, when total transmission power is constant, transmission power per antenna is reduced. As a result, the massive MIMO system is constructed as the specification for low power consuming and operating power amplifier (PA), etc., to reduce radio frequency (RF) component cost, such that it may economically be constructed. In particular, in the multiple antenna transmission system (massive MIMO system), a base station (for example, eNodeB) uses a signal of a user data to form a beam in a direction in which a terminal (for example, user equipment (UE)) is positioned, thereby increasing a transmission signal-to-noise ratio. For example, according to long term evolution (LTE) or LTE-advance (LTE-A) mobile communication standards which are being standardized in a third generation partnership project (3GPP), a signal of a physical downlink shared channel (PDSCH) which is each user data channel forms a beam at the place where a terminal is positioned for signal transmission. However, when a signal is a common channel signal which is a data signal commonly required for all terminals such as synchronous signal (SS), physical broadcast channel (PBCH) to inform system information to all terminals in the radio service area. In this case, the base station needs to omnidirectionally transmit the common channel signal rather than to transmit a common channel signal through beam formation based on the multiple antenna (MIMO antenna) so as to transmit the common channel signal to all terminals within a service area.
In this case, if the base station uses only some antennas without using all the antennas for omnidirectional transmission, the transmission power or outputs of RF stages and antenna parts need to be increased to cover the service area. In this case, expensive RF components such as a high output PA are required and the system needs to be designed to enable a high output.
Therefore, a method for transmitting the common channel signal using all the antennas or at least as many as antennas available in the multiple antenna system (MIMO system) is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.